Gmail bans .exe file attachment

Gmail purposely blocks .exe file attachments as this is a common trick to spread virus, trojan and malware.  Not just only .exe, but other file types like ade, adp, bat, dll, msp, vb, sys, vbs, wsf are also prohibited.  Occasionally, I have to send .exe files to friends who are Gmail users.  I just rename the file to .pdf and attach in the email with the sha1sum of the .exe file before renaming.  On the other side, the recipient just download the attachment, rename it to .exe and then perform a sha1sum check.  Everything works quite well.

It seems not difficult to bypass Gmail's blocking of .exe files.  On the other hand, since Microsoft .exe files have the file signature of 4D5A in the header, I tend to think that it is possible for Gmail to screen out actual executable files instead of just looking at the name of the file extension.